1. Field of the Invention
The invention relates to an apparatus for generating or producing ozone with a high voltage source and at least two spaced plate electrodes having a dielectric positioned between them accompanied by the formation of at least one flow path.
2. Background Art
Ozone is the triatomic modification of oxygen and is inter alia formed under the influence of an electric field. In the case of a so-called silent discharge (corona discharge), oxygen (O.sub.2) is, in part, converted into ozone. The electric discharge brings about a partial cleavage of the O.sub.2 molecules into free atoms which, when meeting uncleaved molecules, become attached to the latter. Electric energy is consumed during ozone formation and the mechanical equivalent of heat for this is 34.5 kcal/mole O.sub.3. On heating, ozone decomposes, so that energy is given off and O.sub.2 is formed. Gas very rapidly decomposes at temperatures above 100.degree. C. or in the presence of catalysts at ambient temperature.
Ozone is much more reactive than oxygen and is consequently an extremely powerful oxidant, which is used in petrochemistry for converting olefins into aldehydes, ketones or carboxylic acid. It is also used as a bleaching agent for organic substances and for sterilizing drinking water and workrooms.
On an industrial scale ozone is generally produced by means of a silent discharge. Oxygen or an oxygen-containing gaseous mixture is passed through a flat or annular gap between two electrodes and an interposed dielectric. In the various known apparatuses and processes for producing ozone, an attempt has been made to increase the ozone yield, while avoiding ozone heating.
German Patent 3 108 563 discloses an apparatus for generating ozone in which means are provided to control the frequency and amplitude of the a.c. voltage generating the electric field, so as to improve the ozone yield. The high voltage generators are operated in the pulse mode or the a.c. frequency is increased, because in both cases an increased ozone yield is obtained. However, the thermal losses also increase, so that when ozone is produced according to the principle of the silent discharge the discharge gaps become heated and this leads to a reduction in the ozone yield.
Apparatuses for producing ozone, also known as ozonizers, operated in the pulse mode suffer from the further disadvantage that the discharge between the two electrodes is punctiform or lenticular as a result of the edge slope, i.e., does not take place on the entire electrode circumference. As a result burn-in holes are formed on the electrodes, so that the ozone yield is reduced and a satisfactory apparatus function is not obtained.
DE-OS 2 853 436 discloses for increasing the ozone yield to create a turbulent flow in the discharge gaps by introducing bodies. However, this leads to a certain increase in the flow channels, so that the field strength must be increased. In addition, relatively high laminar portions remain in the flow interfaces in this process.
DE-OS 2 644 978 discloses an ozonizer based on a high a.c. voltage, while excluding a dielectric. For this purpose it is necessary to have a technically adequately known plate construction, so as to maintain the spacing between two plate electrodes, between which is located in current connection-free manner at least one bipolar electrode.
Finally, German Patent 299 248 describes an apparatus having fixed electrodes, in which the spacing of the electrodes must be kept constant with high accuracy, so as to avoid so-called peak discharges. For this purpose the fixed non-conductor was sprayed with a metal coating, so as to ensure the constant spacing between the electrodes.
The object of the invention is to provide an apparatus of the aforementioned type for the generation of ozone, in which a turbulent flow is formed in simple manner in the flow channels, while simultaneously rendering uniform the surface distribution of the discharge channels for increasing effectiveness,
According to the invention this object is solved in that at least one of the plate electrodes is oscillatable, the plate electrode comprises two layers of electrically conductive material, at least one layer being oscillatable, a material acting in resilient-attenuating manner is positioned between the two layers and the two layers are fixed to permit electrode oscillations.
It is possible with such an apparatus, through the application of a low frequency a.c. voltage and/or a suitable flow rate of the medium to be treated, to make the electrodes oscillate, so that a turbulent flow forms in the flow paths or channels between the electrodes and the dielectric. As a result of the oscillating electrodes there is in particular a separation of the interface in which otherwise normally a laminar flow prevails.
The width of the flow paths and the flow rate are such that the formation of a turbulent flow is guaranteed.
As is known, the nature of the flow (laminar or turbulent) results from the value of the Reynolds number: ##EQU1## in which w=the average flow rate, m/s; d is the tube diameter, m;
.mu.=the dynamic tenacity; kg/m s; PA1 p=the density of the liquid, kg/m; PA1 v=the kinematic tenacity; m/s.
If the flow cross-section is not circular, then the equivalent diameter corresponding to the multiple of the hydraulic radius is inserted in the expression for Re.
The hydraulic radius r represents the ratio of the area of the flow cross-section to the circumference U wetted by the flow: ##EQU2##
For a tube having a circular cross-section, through which there is a full flow, we obtain: ##EQU3##
For a flow of non-circular cross-section one may thus, instead of the diameter, insert the equivalent diameter: ##EQU4##
Generally, in the case of a turbulent flow, the Reynolds number is above 2300 and there is an absolute turbulent flow at Re&gt;10,000.